1. Field of the Invention
The invention relates to backlight control of a liquid crystal display panel.
2. Description of the Background Art
Conventionally, an image is displayed on a liquid crystal display (LCD) panel by turning on a backlight of a liquid crystal display and by appropriately changing a transmittance of light passing through the LCD panel.
When the transmittance of light passing through the LCD panel is changed, a response time of, for example, some milliseconds or some hundred milliseconds is required for a pre-change transmittance to reach a post-change transmittance (target transmittance). Therefore, a backlight is turned on in the middle of the change of the transmittance, an image is displayed for a user before the transmittance reaches the target transmittance. As a result, there was a case where an unclear image, mainly an unclear moving image, was displayed for the user.
Thus, a technology that sets the response time as a predetermined time period, and that turns of the backlight and keeps the backlight off until the predetermined time period passes and turns on the backlight after the predetermined time period passes, has been conventionally known.
However, in a case where a transmittance is changed, when at least one of a pre-change transmittance and a post-change transmittance is different from a subsequent pre-change transmittance and a subsequent post-change transmittance, a response time also changes. Therefore, in the case where a backlight of a LCD panel was turned off until the certain time period set as the response time passed and where the backlight was turned on after the certain time period passed, an image was displayed for the user before the transmittance reached the target transmittance. As a result, there was a case where an unclear and blurred image was displayed for the user.
The following are examples of different response times in which the transmittance starts to change and reaches a target transmittance. For example, as compared to a case where a transmittance that is 100% before a change becomes 70% after the change (where a change of the transmittance is small), in a case where a transmittance that is 100% before a change becomes 0% after the change (where a change of the transmittance is great), the response time is longer.
Moreover, in a case where voltage applied to liquid crystal molecules changes from zero to a value other than zero, the response time is longer than a case where voltage applied to the liquid crystal molecules changes from a value other than zero to zero. In other words, even when change rates at which transmittances change to target transmittances are the same, response times required for the transmittances to change are different.